Previous studies of monkeys will be extended. The effects of intervening experience during which hand preference is maintained or reversed will also be evaluated. 1) Hand preferance during simple reaching will be determined as a function of age. 2) Split-brain animals with optic chiasm and forebrain commissures sectioned will be tested for monocular and binocular recall of a visual discrimination as reported previously for animals with chiasm section alone (26). Animals will be binocularly trained preoperatively and tested for recall postoperatively under monocular conditions. Comparison of postoperative recall through the right and left eye should permit conclusion regarding the retention of the original training by the right and left cerebral hemispheres. Correlations with the hand carrying out most of the responses during training will be attempted in order to determine whether the hemisphere controlling the response during learning is also the one most apt to remember its training to greater degree. 3) Animals with sectioned optic chiasms have been trained to distinguish between two bilaterally symmetrical shapes. They were subsequently tested one eye at a time with two mirror-image shapes, each of oppositely lateralized polarity, with one side resembling the previously rewarded shape and the other side resembling the unrewarded shape ("left and right side positive"). Opposite shapes were preferred with each eye (27). Since vision with each eye after chiasm section was restricted to opposite visual half-fields, normal animals would presumably be subject to conflicting tendencies when faced with the mirror-image discrimination after training upon the symmetrical shapes. Normal animals will be trained and tested in order to determine the distribution of preference for one or the other ("left or right side positive") mirror-image shape and to see whether lateralized preferences correlate with the preferred hand. 4) When viewing with one eye, animals with optic chiasm section pay greater attention to one side of a shape than another (26). Ablations of associated areas will be carried out in an attempt to determine whether or not greater visual attention to one side of a perceived object is due to a central mechanism rather than to visual field defect.